Waste effluent treatment is important to address environmental pollution. Treatment of water is also increasingly important to mitigate problems with scarcity of drinking water. Over the years, many methods have been developed for the treatment of water, such as filtration, centrifugation, precipitation, electrolysis, and adsorption.
Among the methods developed, adsorption of contaminants is a highly cost effective method to remove soluble pollutants, such as heavy metal ions and dyes. Adsorption is a surface phenomenon, and performance of adsorbent technologies may largely be affected by effective surface area of the materials. Therefore, state-of-the-art adsorbent materials are typically in the form of powder or granule to maximize the surface area to mass ratio. Consequently, filtration setup is inevitably required during adsorption and regeneration operations to contain and separate the adsorbent material from treated water, so as to avoid secondary contamination of the treated water by the adsorbent material. This added processing cost of filtration became increasingly significant as smaller and smaller adsorbent materials are employed to increase the surface area for higher adsorptive capacity. Such separation processes also introduce added complexity.
Adsorption technologies using activated carbon, for example, are already in use in the industry, and remain popular due to abundance of the material. However, the activation process of carbon is expensive and the adsorption of the contaminants is essentially a physisorption process. Such a mechanism is challenging in terms of its stability, selectivity, and effectiveness in the removal of bulky contaminants.
The trend towards nanomaterials, such as hollow spheres, nanoflakes, nanorods, and hierarchical nanostructures and nanoparticles, is currently not realized despite discovery and engineering of high performance adsorbents, as fear of leeching and inability to remove such nanomaterials prevent their implementation. The nanomaterials have to be effectively contained or removed after the treatment process. Any failure in containing or removing the nanoparticles increases the risk of introducing nanoparticles into the treated water. This is highly detrimental as nanomaterials can have chronic or acute health effects when ingested. This increases the apprehension towards the use of such adsorption technologies and hinders their widespread adoption. Moreover, high temperatures, surfactants or toxic organic compounds are often needed in the synthesis for the creation of the nanostructures that are not environmentally friendly.
So far, the use of nanomaterials still demands granulation or pre-coagulation to bring the nanoparticles into micron size for possible extraction through filtering. This approach is counter-productive and defeats the initial purpose of using nanomaterials because coagulation inevitably reduces the effective surface area.
In view of the above, there exists a need for an improved method for removing pollutants that addresses or at least alleviates one or more of the above problems.